Igniter composition

ABSTRACT

1. A composition consisting essentially of about 30 to about 85 weight percent of a material selected from the class consisting of polytetrafluoroethylene and polytrifluorochloroethylene; about 15 to about 70 weight percent of a material selected from the class consisting of magnesium, aluminum, boron, titanium, ziroconium, thorium, mixtures thereof and lithium nitride; about 1 to about 10 weight percent of a material selected from the class consisting of potassium dichromate, manganese dioxide, ammonium nitrate and ammonium perchlorate; and from about 1 to about 10 weight percent of a material selected from the class consisting of lead fluoride and sodium fluoride.

United States Patent [191 Julian et al.

[ Aug. 21, 1973 IGNITER COMPOSITION [22] Filed: June 13, 1957 [21] Appl.No.: 665,613

FOREIGN PATENTS OR APPLICATIONS 628,247 8/ 1949 Great Britain PrimaryExaminer-Carl D. Quarforth Assistant ExaminerE. A. Miller Attorneyl(. F.Ross and Q. B. Warner EXEMPLARY CLAIM 1. A composition consistingessentially of about 30 to about 85 weight percent of a materialselected from the class consisting of polytetrafluoroethylene andpolytrifluorochloroethylene; about 15 to about 70 weight percent of amaterial selected from the class consisting of magnesium, aluminum,boron, titanium, ziroconium, thorium, mixtures thereof and lithiumnitride; about 1 to about 10 weight percent of a material selected fromthe class consisting of potassium dichromate, manganese dioxide,ammonium nitrate and ammonium perchlorate; and from about 1 to about 10weight percent of a material selected from the class consisting of leadfluoride and sodium fluoride.

2 Claims, 3 Drawing Figures PATENTEDAUGZI ma 3.75331 1 SHEET 1 0F 3INVENTORS ELMO C. JULIAN FRANK G. CRESCENZO ROBERT C. MEYERS, DECEASED,av BETTE C. MEYERS,exEcuTR|x,

R Y" m/- ATTORNEYS IGNITER COMPOSITION The invention described hereinmay be manufactured and used by or for the Government of the UnitedStates of America for governmental purposes without the payment of anyroyalties thereon or therefor.

This invention relates to a new igniter, more particularly, it relatesto an igniter mixture for gas producing charges such as propellants,fuels and explosives.

The ideal igniter should produce short ignition delays with reproducibleoutput characteristics independent of environmental temperature andpressure conditions without causing damage to any component parts. Inaddition, igniter materials should be sufficiently inert to avoid hazardwhen handling. They should have good surveillance characteristics. Theprincipal igniter materials used in the past have consisted of blackpowder used alone, or a mixture of 80 percent black powder and 20percent magnesium. The above materials are subject to the disadvantagesthat they are highly sensitive to static electricity and friction, thusmaking their handling extremely dangerous. Also, they absorb moisturefrom humid air, this factor adversely affecting their ignitioncharacteristics in that it leads to delayed ignition and completeignition failures. Additionally, the above materials are highlysensitive in their operation to changes in temperature and pressure.Further, mixtures of black powder and magnesium have a tendency tosegregate, thus vitiating the advantages of the combination.

It is therefore an object of this invention to provide an igniter whichhas an acceptable range of ignition time delay.

It is another object of this invention to provide igniter mixtures whichare inert to static electricity, impact and friction. It is anotherobject of this invention to provide an igniter mixture which is inert totemperatures below 400C.

It is another object of this invention to provide an igniter mixturewhich has good surveillance characteristics and which is unaffected inits operation by moisture in the atmosphere.

It is a further object of this invention to provide an igniter whichgives reproducible output characteristics which are independent ofenvironmental temperature and pressure conditions.

It has been found that the above objectives are accomplished by anigniter incorporating a composition comprising a mixture of a materialfrom the class consisting of magnesium, aluminum, thorium, zirconium,titanium, molybdenum, boron and lithium nitride, with a fluorinatedalkene. To this composition may be added oxidizing agents such aslithium perchlorate, potassium dichromate, manganese dioxide andammonium nitrate. Catalytic agents, such as, inorganic fluorides mayalso be added. Examples of these inorganic fluorides are fluorides ofthe alkali metals and lead.

The invention is best understood by reference to the followingdescription taken in connection with theaccompanying drawings herebymade a part of this specification and in which:

FIG. 1 is a cut-away showing of an ignition testing semi-vented bomb,used to test the compositions of the invention;

FIG. 2 is a horizontal cross-section of a two inch steel static firingmotor for testing the ignition of end burning propellent charges; and

FIG. 3 is a typical pressure-time graph showing the igniter performancecharacteristics of interest obtained from test firing the two inchsemi-vented bomb of FIG. 1.

The bomb of FIG. 1 comprises generally an internal pressure chamber inwhich the propellent grain is ignited by means of a conventional squiband the igniter composition of this invention. The pressure chamber isprovided with means for measuring internal pressures at various timesand intervals of space along the bomb. Referring to FIG. 1, the outercase of the bomb is represented by numeral 10 and the internal pressurechamber by the numeral 11. The case 10 is provided with threaded endplugs 12 and 13 for engagement with the ends of case 10. The end plug 12contains the igniter assembly and the end plug 13 contains the pressurerelief assembly. A three inch section of an internal burning, externallyinhibited, star perforated propellent grain is shown at 14. The grainhas an outside diameter of 1.9 inches. The igniter material is shown at15. For igniting the igniter material 15 a conventional squib isprovided at 16 which in turn is provided with a pressure seal electricallead 17. For measuring pressure in the chamber at various intervals oftime and space, pressure taps 18, 19, 20, 21, and 22 are provided. Thesetaps are connected by hydraulic lines to Wiancko conventional typepressure gages. A cap 23 is provided for pressure tap 18 to preventpressure leak when the device is inoperative. Rupture discs 26 and 27designed to rupture at predetermined pressures are provided as shown.For adjusting the distance between propellent grain and igniter,removable collars 28 are provided in the pressure chamber. Athermocouple assembly 29 is supported by end plug 13.

In operation of the test bomb, a propellent charge 14 is placed in theinner cavity 11 of the bomb as shown, and the igniter composition 15 ofthe invention is inserted in the case 4 inches from the propellant l4and adjacent the squib 16. After the pressure gages have been connectedto suitable recorders, the igniter is ignited by introduction of currentto the squib 16 through electrical lead 17. During the process ofignition of the squib, igniter and propellant, pressure-timemeasurements are recorded.

Referring to FIG. 2, there is shown a static testing rocket motor havingan outer casing 30 and provided with head end closure 31. Head endclosure 31 is sealed to the rocket body by means of threaded ring 32 attached to the case 31 by fillet 33, and internally threaded cap 34 asshown. 0 ring 35 is provided to furnish a gas tight seal. The rocketnozzle is shown at 36 having an exhaust port 37. The nozzle 36 isattached to the rocket body by means of threaded ring 38 secured to theouter casing or rocket tube 30 by means of fillet 39, and internallythreaded cap 40. Nozzle shear ring 41 is provided as shown. The endassembly is made gas tight by means of O ring 44. Pressure plugs 46 areprovided for measuring pressure in the cavity aft of the rocket grain. Aseries of these plugs located circumferentially in the outer casing maybe used. Spacing ring 47 is provided for holding the grain secure. Fortesting the igniter, a double base end burning propellent grain 48having an outer inhibiting coating 49 is located in the rocket motorchamber as shown. The grain is provided with a conical shaped burningsurface 50. The igniter material of the invention in a plastic bag 52with a conventional squib 53 in proximity thereto is positioned asshown. Electrical leads 54 are provided as shown for conducting currentfrom a source not shown to squib 53. In operation of the motor, currentis introduced to ignite the squib, igniter material and propellant inturn. Internal pressure is measured by means of the pressure plugs 46which are hydraulically connected to pressure gages.

Referring to FIG. 3, there is shown a typical pressuretime graph used topresent important igniter test data obtained by testing compositions ofthe invention in the test device of FIG. 1. The compositions areoperative as igniter materials under actual operating conditions. ln thegraph, pressure is plotted on the ordinate against time delay inmilliseconds on the abscissa. The legend for the numerals is shown onthe drawing. Squib time is the interval of time between the applicationof current to fusion of the bridge wire in the squib. lgniter time isthe time elapsing from fusion of the bridge wire to ignition of theigniter or until the first indication of initial pressure, this laterindicating the ignition of the igniter. The ignition duration is thetime between ignition of the igniter and ignition of the propellant andis indicated on the graph by the inflection of the pressure time curveas indicated by the numeral 3. The propellant ignition delay is the sumof the igniter time and the ignition duration as represented by thenumerals 2 and 3 on the graph. This is the most significant factor inthe evaluation of igniter mixtures. Numerals 5, 6, 7 and 8 representsupplementary pressure information shown on the graph.

The invention is illustrated by the examples included in Tables 1-4,inclusive, which are illustrative only of the invention but not limitingthereof. Tables 1 and 2 present comparative results of ignition testsperformed on black powder, black powder-magnesium mixture, and apolytetrafluoroethylene-magnesium mixture of the invention. Tables 3 and4 present examples of ignition mixtures of the invention and test datatherefor. The data for the examples was obtained with the ignitiontesting, semi-vented bomb of FIG. 1.

The compounding of the igniter mixtures is illustrated by the following:Metal powder 100 mesh or finer was added to powdered Teflon polymer of50 mesh or finer in ratios of 50 to 800 percent of the stoichiometricquantities. These materials were then thoroughly mixed. They may beblended, rolled or treated in a signal blade mixer. Alternate methods ofmaking the mixtures is as follows: Teflon is reduced to less than 5micron particle size by techniques well known in the art and introducedto a Waring blendor. An inert solvent such as acetone or a hydrocarbonis added and the mixture blended for seconds in the blendor. Thismaterial is transferred to a suitable vessel where the metal is addedand the mixture is stirred for 5 minutes. The material is then filteredto remove the bulk of the solvent and transferred to a mixer where theremainder of the components are added. Complete grinding followed byfurther mixing completes the compounding.

The fluorocarbon compound is a polymeric halogenated alkene, preferably,polytetrafluoroethylene or polytrifluorochloroethylene or mixturesthereof. Other fluorinated alkenes may be used, such as, the fluorinatedhigher alkenes. By the term fluorinated as used in this specificationand claims is meant either totally or partially fluorinated. Thepolytetrafluoroethylene may have a molecular weight range from 100,000to 9,000,000. This compound is known commercially as Teflon and itschemical composition is published in the literature. Thepolychlorotrifluoroethylene may have a molecular weight range from 303to 10,000. This compound is known commercially as Kel-F. It may be usedin the composition in liquid, solid or waxy form depending upon theamount of plasticization which is to be effected by its use in non-solidfonn. Plasticization to a degree, may be effected through the use ofliquid polymers such as KEL -F polymer oil of various molecular weights.A portion of the solid polymer may thus be replaced by a chemicallyequivalent weight of the liquid polymer. When used in solid form thefluorocarbon compound is a powder of less than 20 mesh particle size.

The following is an example of compounding the composition whenplasticization is required. The metal powder, mesh or finer, is added tosomewhat less than the intended quantities of the powdered solidpolymer, 50 mesh or finer. Enough liquid polymer to realize the intendedratio of total polymer to powdered metal, 50 200 percent of thestoichiometric quantities, is added. The liquid polymer may be added inthe form ofa solution in a solvent such as benzene or methylenechloride. In this case the solvent must be removed by evaporation. Thematerial may be mixed in a sigma blade mixer.

As respects the metals used, the heat of formation of the metal-fluorinebond must exceed 67 kilocalories per gram molecule of the condensedhalide. As the examples show, the nitrides of these metals may be used.The carbides and hydrides, having similar chemical properties andsimilar heats of formation as the nitrides may be used also. The metalsand their compounds may be in divided form of less than twenty mesh, orpart of the finely divided metal may be replaced by wire of 0.0020inches in diameter or granules of 20 25 mesh particle size.

Oxidation of one of the reaction products, carbon, may be effected bythe addition of an oxidant, such as, ammonium nitrate, or lithiumperchlorate in amounts of not more than 10 percent by weight. A smallincrease in gas production is thus effected. The oxidant may be added tothe mixture without affecting the polymer-metal ratio. The oxidant maybe in powdered or pellet form.

The propellants used to test the igniter composition are the double basepropellants, N-S and X-l l. A representative N-S composition is asfollows:

Component Wt. Percent Nitrocellulose 12.6%N) 50.00 Nitroglycerin 34.9Diethyl Phthalate 10.50

Z-Nitrodiphenylamine 2.00 Lead 2-Ethyl Hexoate L20 Lead Salicylate 1.20Candelilla Wax 0.20

A representative X-ll composition is the following:

Component Wt. Percent Nitrocellulose (12.6%N) 50.00 Nitroglycerin 33 .lDiethyl Phthalate 12.4 Z-Nitrodiphenylamine 2.0 Lead Salicylate 1.2 LeadB-resorcylate l.2 Candellia Wax 01 Carbon Black +0.05

As stated previously, the percentage of metal to fluorocarbon which maybe used is preferably from about 6 to about 800 percent of thestoichiometric. The presame composition and ignition delay valuesobtained ferret] percentage range is from about l5 to about show adefinite relationship between the composition percent by weight of metaland about 30 to about of the mixture and its heat of explosion.Variation in percent by weight of fluorocarbon. ignition time delayresults from the extreme conditions TABLE I Summary of PerformanceCharacteristics of Igniter Materials Test Fired at 65 F. in 2.0-InchDiameter Experimental Test Vehicles with N -5 Propeliant PropellantInitial Initial Propellant Propeliant Igmter Squib Ignrter Ignitionignition peak rate of presignition rate of pres- Average charge time,time, duration, delay, pressure, sure rise, pressure. suro rise, heat ofIgniter material wt. msec. msec. msec. msec. p.s.i. p.s.i./msec. p.s.i.p.s.i./msec. explosion Black powder 3. 0 14. 0 2. 0 12 14 326 137 51050. 6 700 Black powder, 80%Mg, 20%... 3. 0 9.0 20. 0 3 23 460 213 50543. 7 850 Polytetratluoroethylene, 67%- TABLE II Test Made at 65 F. in2.0 Diameter Inch Experimental Test Vehicle with X-ll PropcliantPropellant Initial Initial Propcliant Propeilant Igniter Squib IgniterIgnition ignition peak rate of presignition rate of pres- Average chargetime, time, duration, delay, pressure, sure rise, pressure, sure rise,heat of Ignitar material wt. msec. msec. msec. msec. p.s.i. p.s.i./msec.p.s.i. p.s.i./msec. explosion Black powder 3. 0 18. 6 8. 7 13. 4 22. 1368 643 87 700 Black powder, 80%Mg, 20%." 3. 0 18. 7 8. 2 10. 2 18. 4325 94 581 111 850 Poiytetraiiuoroeth yiene, 67%

TABLE III Three gram charge weights were used. Tests were run at 06 F.The propellent charge was spaced 4" from the ignitcr. The. examples areglvon in percentage composition by weight Component (wt. percent)Example No. Magnesium Boron PTFE PCTFE NaF KzCraOr 11.15. P.I.D

10. 0 7. 5 7. 5 1, 281 32. 0 10.0 7. 5 7. 5 1, 597 17. 5 10.0 7. 5 7. 51, 8-16 14. 5 l0. 0 7. 5 7. 5 l 378 4. 5 10. 0 7. 5 7. 5 1, 059 59.1 10.0 7. 5 7. 5 1, 347 "6 I 2. 5 2. 5 l, 964 14 5LEDoENn.-P'IFE=Polytetrafluorocthylene;PCTFE=Polychlorotritluoroethylene; H. E.=Heat of explosion in caloriesper gram; P. I. D.=Propeiiant ignition delay in milliseconds.

TABLE IV A three gram charge weight was used. Mixtures were tested at 65F. with tho propellant being spaced 4 from the igniter. The examples aregiven in percentage compositions by weight Component (wt. percent)Example No. Th Zr Ti Mo Al LiaN PIFE KaCrzQr NBF PbFz LlClOi H.E. P.I.D.

it will be noted that all data, with the exception of the under whichthe tests were made. it will lac-noted from heat of explosion tests, wastaken at temperatures of 60 the results oiTables l and ii that thepropellant ignition 65 F for three gram charge weights. The igniter wasdelay obtained with magnesium-Teflon mixtures is as spaced a distance offour inches from the propellent good as that obtained with the ignitioncompositions of charge. Test firings were conducted at low temperatheprior art, that is, black powder used alone and black tures with smalligniter charge weights, as these condipowder-magnesium mixture. Forpropellant ignition in tion's indicate successful functioning at extremecondi- 65 general, it is to be noted that differences in propellanttions' as well as extend the difference in the ignition ignition delaywhen the total time is less than 35 millitime delays of similarcompositions. Examples 1 seconds are insignificant as any ignition delayunder 35 through 5 in Table iii show varying proportions of themilliseconds is highly acceptable. The advantages of the ignitionmixtures of the present invention over prior art ignition mixtures stemfrom other properties. It will be noted from all the examples that theheat of explosion of the igniter compositions of this invention can beadjusted to fit the circumstances by choice of the metal used. inexample 8 of Table IV, a composition is shown in which the heat ofexplosion is only 647 calories per gram. This composition could be usedin applications wherein heat damage to surrounding metal parts is to beavoided. It is to be noted that in all examples, with the possibleexception of examples and 8 of Tables Ill and IV, respectively, anacceptable ignition time delay is obtained. The examples show that theigniter mixtures of the invention produce extremely high energy output,and have reproducible output characteristics under severe conditions.The mixtures were tested and found to be inert to shock, friction, orstatic electricity, and insensitive to temperatures of 400C or less. Themixtures are simple to manufacture from readily obtainable materials;they are not subject to segregation, they are non-toxic and theiroperation is not affected by moisture and high humidity. The mixturesare compatible with propellent and explosive compositions in general,and can be assembled in contact with the propellant. This is in contrastto black powder which is in compatible with double base propellants, forexample, and must be assembled in a cannister to avoid contact with thepropellant, as well as to prevent absorbtion of moisture from theatmosphere by the black powder. To test the inertness of the mixtures tostatic electricity a spark from a spark coil was discharged through theignition mixtures placed in the spark gap without ignition of thepowder. Representative samples of the ignition mixtures were subjectedto temperatures at 400C for four hours in a muffle furnace with no signsof ignition. Drop tests performed on representative mixtures indicatethat they are highly insensitive to shock. For example, only 50 percentignition was obtained in drops of 85 centimeters with a two kilogramweight. As will be noted from the compositions of the examples,oxidizing agents such as potassium dichromate may be added. Catalyticagents, such as, fluorides of the alkali metals and lead fluoride mayalso be incorporated in the mixtures. It was noticed that a slightimprovement was obtained by the combinations of oxidizing agent andcatalytic agent. The effect of the catalytic agent is believed to be dueto probable activation of the surface of the metal, thus enhancing itsreaction with the fluorinated compound.

While the effectiveness of the ignition compositions of the inventionhave been illustrated by the ignition of double base propellants havinga nitroglycerinnitrocellulose base, they are by no means limited to thisapplication as they are equally applicable to the ignition of otherpropellants and explosives in general.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

l. A composition consisting essentially of about 30 to about 85 weightpercent of a material selected from the class consisting ofpolytetrafluoroethylene and polytrifluorochloroethylene; about 15 toabout weight percent of a material selected from the class consisting ofmagnesium, aluminum, boron, titanium, zirconium, thorium, mixturesthereof and lithium nitride; about t to about 10 weight percent of amaterial selected from the class consisting of potassium dichromate,manganese dioxide, ammonium nitrate and ammonium perchlorate; and fromabout 1 to about 10 weight percent of a material selected from the classconsisting of lead fluoride and sodium fluoride.

2. The composition according to claim 1 wherein the material selectedfrom the class consisting of magnesium, aluminum, boron, titanium,zirconium, thorium, mixtures thereof and lithium nitride has a particlesize which does not exceed 20 mesh.

1. A COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 30 TO ABOUT 85 WEIGHTPERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OFPOLYTETRAFLUROETHYLENE AND POLYTRIFLUOROCHLORETHYLENE, ABOUT 15 TO ABOUT70 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OFMAGNESOIUM, ALUMINUM, BORON, TITANIUM ZIROCONIUM, THORIUM, MIXTURESTHEREOF AND LITHIUM NITRIDE, ABOUT 1 TO ABOUT 10 WEIGHT PERCENT OF AMATERIAL SELECTED FROM THE CLASS CONSISTING OF POTASSIUM DICHROMATE,MAGANESE DIOXIDE, AMMONIUM NITRATE AND AMMONIUM PERCHLORAGE, AND FROMABOUT 1 TO ABOUT 10 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASSCONSISTING OF THE LEAD FLUORIDE AND SODIUM FLUORIDE.
 2. The compositionaccording to claim 1 wherein the material selected from the classconsisting of magnesium, aluminum, boron, titanium, zirconium, thorium,mixtures thereof and lithium nitride has a particle size which does notexceed 20 mesh.